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# Official Edexcel C3 Discussion Thread watch

1. (Original post by [email protected]@y)
@ unamed cheers but i've already done the Solomon papers.

I'm assuming that they will increase the difficulty because of the A*.90% plus
I don't think so. I'm assuming that they will fill it completely with proofs and not with any graphs and so then I shall be happy.
2. Does anyone have a list of functions whose graphs we have to know?

Like e^x, trigs, inverse trigs, lnx, 1/x, x^2, squareroot(x), x^3

Are there anymore?
3. On Jan 07, question 6 a, the mark scheme doesn't say what the domain is. I got f^-1(x) > 0, anyone else?
4. (Original post by Doughboy)
Does anyone have a list of functions whose graphs we have to know?

Like e^x, trigs, inverse trigs, lnx, 1/x, x^2, squareroot(x), x^3

Are there anymore?
Um. No more, I don't think. Exciting stuff, isn't it?

oo, wait I remember - the straight line! !
5. (Original post by Woody.)
On Jan 07, question 6 a, the mark scheme doesn't say what the domain is. I got f^-1(x) > 0, anyone else?
why's it greater than 0? I'd say it was all real numbers.

edit(again): sorry, I was doing the range for some odd reason.
6. so do we reckon this paper will be as "easy" as last year, or are we expecting it to be a little/lot more difficult?
7. (Original post by unamed)
why's it greater than 0? I'd say it was all real numbers.
Well because the range of the inverse is less than 2. And then when you put the inverse equal to two you have to have a number greater than zero? I'm not sure, this is only my vague reasoning, you may well be correct.
8. (Original post by Mattjames)
so do we reckon this paper will be as "easy" as last year, or are we expecting it to be a little/lot more difficult?
more difficult - they've been easy for far too long, I think!
9. (Original post by unamed)
more difficult - they've been easy for far too long, I think!
im hoping theyll be about the same difficulty for at least the first two thirds, but then i reckon theyll unleash hell on us with Q7 & 8 for the A* people. but they'll keep it as easy for the first lot so that marks arent extremely low.
10. (Original post by Woody.)
Well because the range of the inverse is less than 2. And then when you put the inverse equal to two you have to have a number greater than zero? I'm not sure, this is only my vague reasoning, you may well be correct.
but the range of f(x) is all real numbers. so, the domain of the inverse must be all real numbers.
Oh and I think it is R because on my copy, it comes out as a little box.
11. (Original post by Mattjames)
im hoping theyll be about the same difficulty for at least the first two thirds, but then i reckon theyll unleash hell on us with Q7 & 8 for the A* people. but they'll keep it as easy for the first lot so that marks arent extremely low.
That sounds like a reasonable paper. I'd like one like that. Let's hope the examiner thinks like you!

or it might be like the C2 paper.
12. (Original post by unamed)
Um. No more, I don't think. Exciting stuff, isn't it?

oo, wait I remember - the straight line! !
And the modulus function (which is an extension of the straight line). Lolzer.
13. (Original post by unamed)
the jan 07 paper is icky.
Ok, so it's not just me then...I am really nervous. Worst nightmare is opening the question paper and not being able to do question 1.
14. (Original post by unamed)
That sounds like a reasonable paper. I'd like one like that. Let's hope the examiner thinks like you!

or it might be like the C2 paper.
what was the C2 paper like?

Also: quick question on self-inversing functions.

how do you do f-1 (x) of things like 10-x/x+2 ? a quick walkthrough would do me the power of good here
15. (Original post by gottastudy)
Ok, so it's not just me then...I am really nervous. Worst nightmare is opening the question paper and not being able to do question 1.
nah, I had my nightmare last night: a cat was sitting in front of me while I was doing the paper - I froze, unable to complete it.

And then, now, I heard a buzzing sound - though I was going crazy. luckily it was just an annoying fat fly.
16. (Original post by Mattjames)
what was the C2 paper like?

Also: quick question on self-inversing functions.

how do you do f-1 (x) of things like 10-x/x+2 ? a quick walkthrough would do me the power of good here
C2 was different - some found it hard, some thought it was easy.

let y= 10-x/x+2
so you then get:
xy+2y=10-x
x+xy= 10-2y
x(1+y)=10-2y
x=10-2y/1+y

therefor f^-1(x)= 10-2x/1+x
17. (Original post by unamed)
C2 was different - some found it hard, some thought it was easy.

let y= 10-x/x+2
so you then get:
xy+2y=10-x
x+xy= 10-2y (THIS)
x(1+y)=10-2y
x=10-2y/1+y

therefor f^-1(x)= 10-2x/1+x
awesome! I didnt think of (THIS - bit in quote) at all! good luck tomorrow
18. (Original post by unamed)
but the range of f(x) is all real numbers. so, the domain of the inverse must be all real numbers.
Oh and I think it is R because on my copy, it comes out as a little box.
But isn't it f(x)'s domain all the real numbers that are greater than two?
19. (Original post by Mattjames)
awesome! I didnt think of (THIS - bit in quote) at all! good luck tomorrow
welcome! Good luck to you too!

(Original post by Woody.)
But isn't it f(x)'s domain all the real numbers that are greater than two?
No, it's all the real numbers less than 2. That would be f^-1(x)'s range.
20. (Original post by unamed)
welcome! Good luck to you too!

No, it's all the real numbers less than 2. That would be f^-1(x)'s range.
Okay thanks, I think I get it now, drawing it out helps a lot. Cheers.

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